Carcinogenic risk, influencing factors

We also might be accused of creating a highly artificial situation, because the cells of genetically homogeneous animals held under strict laboratory controls do not experience nearly the number and type of host and environmental influences experienced by people exposed to the same chemical. Perhaps the most that can be said about chemicals that are carcinogenic in laboratory settings is that they may, under some conditions, increase the risk of cancer in humans. Their relative importance in cancer development depends upon many other factors not accounted for in the laboratory experiment. 

The Royal Commission on Environmental Pollution reported in 1996 that it was not aware of any study that provided firm evidence of adverse effects of contaminated land on health.10 However, the potential for health effects is real. Exposure to chemicals is a risk factor for several diseases and the International Agency for Research on Cancer has classified over 70 chemicals as human carcinogens, 60 as probable and more than 200 as possible carcinogens.11 There is evidence of an environmental influence in human diseases such as cancer,12 including geographic variation in cancer incidence in migrant populations, occupational studies and animal experiments. A number of studies also appear to suggest an association between other health effects and exposure to environmental chemicals. There are thousands of sites contaminated with hazardous chemicals with the potential to expose human populations. In the USA, the ATSDR has estimated that 46 % of the assessed National Priority List sites represent an actual hazard to health.13... 

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